36-WG11/Milan/102
R. Suzuki, WL Vosloo
October, 2001
Annex A: Measurement of ESDD and NSDD
A.1. Introduction
When anti-pollution design of the insulator is made, it is indispensable to determine
pollution degree. The pollution degree is generally determined by measuring
equivalent salt deposit density (ESDD) on the insulators which are removed from the
existing transmission lines and/or field testing stations. In addition to ESDD, nonsoluble material deposit density (NSDD) should be measured, especially in case that
much dust or sand is estimated to accumulate on the insulator surface in such an area
as desert or industrial factories. This Appendix describes how to measure ESDD and
NSDD, and how to make chemical analysis of the pollutants.
For site pollution severity measurement purposes we standardise the measurements
by using a string of 7 reference cap and pin insulators. The unenergised insulator
string is located at a height as close as possible to that of the line or busbar insulators.
Each disc of the insulator string is monitored at a defined interval e.g. every month,
every three months, each year, after two years, etc.
Figure A1: ESDD string
A.2. Necessary equipment to measure pollution degree
The following equipment is necessary for the measurement of both ESDD and NSDD.
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Distilled water/demineralized water
Measuring cylinder
Surgical gloves
Plastic cling wrap
Labeled container
Washing bowl
Absorbent cotton/brush/sponge
Conductivity meter
Temperature probe
Filter paper
Funnel
Desiccator/drying oven
Balance scale
A.3 Pollution collection methods for ESDD and NSDD measurement
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The surfaces of the insulator should not be touched to avoid any loss of pollution.
Put on clean surgical gloves.
A container, a measuring cylinder, etc. shall be washed well enough to remove
electrolyte prior to the measurement.
A.3.1 Procedure using a swab technique
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Distilled water of 100 - 300 cm3 (or more if required) shall be put into labelled
containers and absorbent cotton shall be immersed into the water (other tools such
as a brush or a sponge could be used). Conductivity of the water with the
immersed cotton shall be less than 0.001 S/m.
The pollutants shall be wiped off separately from the top and the bottom surfaces of
a cap and pin type insulator with the squeezed cotton. In the case of a long-rod or
a post insulator, pollutants shall usually be collected from a part of the shed as
shown in Figure A.2.
The cotton with pollutants shall be put back into the labelled containers as shown in
Figure A.2. The pollutants should be dissolved into the water by shaking and
squeezing the cotton in the water.
Wiping shall be repeated until no further pollutants remain on the insulator surface.
If pollutants remain even after wiping several times, pollutants shall be removed by
a spatula, and be put into the water containing the pollutants.
Attention should be taken not to lose the water. That is, the quantity shall not be
changed very much before and after collecting pollutants.
Figure A.2: Wiping of pollutants on insulator surface
A.3.2 Procedure using washing technique
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Cover the cap and pin respectively with plastic cling wrap without covering the
insulator surface.
Ensure that the bowl, which the discs are to be washed in, is clean.
Measure down 500 - 1000 cm3 of distilled water (<0.001 S/m) and pour into bowl.
Place the test insulator on its cap in the water and wash the non-ribbed surface
with gentle hand strokes up to the rim.
Gently shake off any remaining water remove insulator from bowl and pour water
into a labelled container. Take care that all deposits are removed from bowl.
Rinse and clean bowl.
Measure down 500 - 1000 cm3 of distilled water (<0.001 S/m) and pour into bowl.
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Place the same insulator as mentioned above on its cap in the bowl and gently
wash pollution off the ribbed surface with gentle hand strokes.
Pour water in second labeled container taking care again that no deposits remain in
the bowl.
A.4 Determining ESDD and NSDD
A.4.1 ESDD calculations
The conductivity and the temperature of the water containing the pollutants shall be
measured. The measurements are made after enough stirring of the water. Short
stirring time, e.g., a few minutes, is required for the high solubility pollutants. The low
solubility pollutants generally require longer stirring time, e.g., 30 - 40 minutes.
The conductivity correction shall be made using the formula (1). This calculation is
based on Clause 16.2 and Clause 7 of IEC Standard 60507.
σ 20 = σ θ [1 − b(θ − 20)]
θ is the solution temperature (C).
σ θ is the volume conductivity at temperature of θ C (S/m).
σ 20 is the volume conductivity at temperature of 20C (S/m).
b is the factor depending on temperature of θ , as obtained by the formula
(2), and as shown in Figure A.3.
b = −3,200 × 10 −8 θ 3 + 1,032 × 10 −5 θ 2 + −8,272 × 10 −4 θ + 3,544 × 10 −2
(2)
0,035
0,03
b (Factor depending on
temperature θ)
where:
(1)
0,025
0,02
0,015
5
15
25
35
θ (solution temperature), C
Figure A.3: Value of b
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The ESDD on the insulator surface shall be calculated by the formulas (3) and (4). This
calculation is based on Clause 16.2 of IEC Standard 60507. The relation between σ20
and Sa (Salinity, kg/m3) is shown in Figure A.4.
where:
Sa = (5,7σ 20 )1, 03
(3)
ESDD = Sa • V A
(4)
σ 20
is the volume conductivity at temperature of 20C (S/m).
ESDD is Equivalent salt deposit density (mg/cm²).
V
is the volume of distilled water (cm³).
A
is the area of the insulator surface for collecting pollutants (cm²).
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Sa , kg/m3
0,1
0,01
0,001
0,001
0,01
0,1
σ20, S/m
Figure A.4: Relation between σ 20 and Sa
Notes:
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1) For a close ESDD measurement in the range of 0.001 mg/cm , it is recommended to use
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very low conductivity water, e.g., less than a few 10 S/m. Normal distilled/demineralized water
less than 0.001 S/m also can be used for this purpose by subtracting the equivalent salt amount
of the water itself from the measured equivalent salt amount of the water containing pollutants.
2) Quantity of the distilled/demineralized water depends on kind and amount of pollutants.
Large quantity of water is recommended for measurements of very heavy pollution or low
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solubility pollutants. In practice, 2-10 litres of water per m of the cleaned surface can be used.
In order to avoid underestimating the amount of pollutants, the quantity of the water would be so
increased to have the conductivity less than around 0.2 S/m. If very high conductivity is
measured, there might be some doubt of remaining pollutants not dissolved due to small
amount of water.
3) Stirring time before conductivity measurement depends on kind of pollutants. For low
solubility pollutants, conductivity is measured at some interval with time up to about 30 - 40
minutes and is determined when the measured values level off. To dissolve pollutants quickly,
special methods such as boiling method and ultrasonic method can also be used.
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A.4.2 NSDD calculations
The water containing pollutants after measuring ESDD shall be filtered out by using a
funnel and pre-dried and weighed filter paper (grade xxx).
The filter paper containing pollutants (residuum) shall be dried, and then be weighed as
shown in Figure A.5.
The NSDD shall be calculated by the formula (5).
NSDD = 1000(W f − Wi ) / A
where:
(5)
NSDD is non-soluble material deposit density (mg/cm2).
is the weight of the filter paper containing pollutants under dry condition
Wf
Wi
A
(g).
is the initial weight of the filter paper under dry condition (g).
is the area of the insulator surface for collecting pollutants (cm2).
Figure A.5: Procedure of measuring NSDD.
Note:
The quantitative chemical analysis would be made on pollutant solution and residuum
after the measurement to identify chemical components of the pollutants. The analysis results
might be useful for close examination of pollution conditions.
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